1. Field of the Invention
This invention relates to an image forming apparatus of the electrophotographic type or the electrostatic recording type, and particularly to an image forming apparatus of the digital type forming an image on the basis of an image signal.
2. Related Background Art
For example, an image forming apparatus, such as an electrophotographic printer, effects selective exposure on an electrophotographic photosensitive member, e.g. a photosensitive drum uniformly charged by a charger, by exposure means to thereby form a latent image, visualizes this latent image into a toner image by a developer (hereinafter referred to as the xe2x80x9ctonerxe2x80x9d) contained in a developing device and also, transfers this toner image to a recording medium and effects image recording. In such an image forming apparatus, it has heretofore been practiced to detect the residue of toner in the developing device by the use of detecting means.
Also, in the image forming apparatus as described above, each time the toner is exhausted, the supply of the toner into the developing device must be effected, but this work of supplying the toner is not only cumbersome, but also results in contamination. Also, the maintenance of the apparatus can be done only by a professional serviceman and has often involved inconveniences to a user.
So, a cartridge comprising a photosensitive drum, a charger, a developing device, a cleaning portion, etc. united into an integral structure has been put into practical use. In such an apparatus, a user loads the apparatus body with such a process cartridge to thereby make the supply of a toner or the interchange of a part such as a photosensitive drum which has come to the end of its service life possible and thus, maintenance becomes easy.
On the other hand, in an image forming apparatus of such a cartridge type, when the toner in the cartridge has become exhausted, it is necessary to interchange the cartridge. Accordingly, heretofore, detecting means for informing the user of the interchange of the cartridge has been provided in a developing device containing toner therein. As the detecting means, there is, for example, one of the piezoelectric sensor type, the magnetic sensor type or like type, but when an AC bias is applied to a developing sleeve for supplying a toner to a photosensitive drum, use is usually made of an antenna sensing type in which a metallic bar (antenna) is disposed in proximity and in parallel with the developing sleeve and the amount of remaining toner in the developing device is detected by a change in electrostatic capacity.
However, such a residue detecting system only indicates the exhaustion of the toner, and does not prepare the user for the replenishment of toner and the use of a substitute cartridge, and therefore could be improved.
It is also conceivable to detect the state when the toner is being exhausted, but this will complicate the detecting mechanism.
It is an object of the present invention to provide an image forming apparatus which can indicate the residue of toner before the toner becomes deficient.
It is another object of the present invention to provide an image forming apparatus in which the approximate amount of toner can be known to a user.
It is still another object of the present invention to provide an image forming apparatus having:
an image bearing member;
electrostatic image forming means for forming an electrostatic image basd on an image signal on the image bearing member;
developing means for developing the electrostatic image on the image bearing member;
deficiency detecting means for detecting the deficiency of a toner in the developing means;
integrating means for integrating the number of image signals; and
residue indicating means for indicating the residue of the toner before the deficiency detecting means detects the deficiency of the toner, on the basis of the integrated amount by the integrating means.
Further objects of the present invention will become apparent from the following description.